The present disclosure relates to a passenger seat, or “seating unit,” such as an aircraft passenger seat, with a dynamic breakover assembly.
Aircraft passenger seats must be designed and constructed according to government regulations and aircraft manufacturer specifications. Virtually every aspect of seat design is thus constrained by requirements imposed by safety, weight and cost considerations. Within these limits the seat must also be aesthetically pleasing, comfortable to a seated passenger, and functional for the passenger as well as airline maintenance, repair and cleaning crews.
Regulatory requirements for aircraft components in the US are based on Title 14 of the Code of Federal Regulations (CFR) Part 25, which sets out standards for aircraft airworthiness. For aircraft passenger seats, sections 25.561 and 25.562 of Title 14 specify requirements for seat structures that may give passengers a reasonable chance of escaping serious injury in a minor crash landing situation.
Main cabin or “coach” class seats are typically constructed with a seat bottom frame (bottom chassis) formed from two or more leg modules and section assembly modules joined together by several beam elements that connect the leg modules and section assembly modules in spaced-apart relation to each other, and collectively form a so-called “ladder frame assembly.” A seat bottom unit is mounted on the ladder frame assembly. The seat bottom unit is usually stationary. A seat back unit is typically pivotally-mounted between two of the section assembly modules so that the angle of the seat back unit can be controlled for comfort, safety and passenger ingress and egress past the rear of the seat. Because of the relatively short pitch between rows of seats, the normal range of movement of the seat back unit is relatively small. The degree of rearward, recline movement is constrained by the position of the rearward row of seats and the requirement to leave the passenger seated behind a particular seat with sufficient room to enter and exit his or her own seat and use the meal tray. The degree of forward movement of the seat back unit is typically limited to a position where the seat back is in a “full upright” position for take-off and landings, and for meal service.
Passenger seats are typically designed whereby the seat back will not move beyond these positions under normal circumstances (including abuse loads). However, provision must also be made for the abnormal situation where severe G-force loads may propel a passenger forward toward the seat back directly in front of them. In such cases, the seat back must be allowed to fold over (breakover) the seat bottom in a controlled manner in order to minimize or reduce injury to a passenger who may be thrown against the seat back during an emergency deceleration (high G-force) event.
For aircraft passenger seats, 14 CFR § 25.562 requires that for a high G-force event (16 Gs), where head contact with seats or other structures may occur, some type of protection must be provided so that the so-called “Head Injury Criterion” (HIC) does not exceed 1000 units. 14 CFR 25.785 has a primary goal of protecting occupants from serious injury during landing condition, including injurious interactions of the head and neck (ref ANM-115-17-002). Conventional methods to generate a low HIC score typically involve either spacing passenger seats far enough apart so that a passenger's head will not make contact with the seat in front of him or her (severely limiting options for seating arrangements which increase the number of seats within the cabin), or building a breakover mechanism into the seat back. In breakover mechanism designs, breakover may occur when a passenger impacts the fore seatback using a force capable of breaking a weak or sacrificial component (e.g., breakable bushing part, shear pin, etc.), which was purposely built into the seat structure, allowing the seat back to begin to tilt forward upon impact. The movement of the seat back in response to a passenger impact may dissipate energy and lower the HIC score. However, these breakover mechanisms can also impact neck injury potential. For example, a reduction in HIC score may not always translate to a reduction of neck injury potential and can even increase the neck injury potential. Therefore, a proper balance in breakover design must be achieved in order to satisfy both requirements. In addition to the HIC score and neck injury potential, damage done to the seat back during a high G-force event must not prevent passenger egress or harm the passengers after an event. For example, the seat must stay largely intact and no sharp edges may occur. Furthermore, in some passenger seat configurations, there may also be neck injury criteria. As described above, the prior art breakover mechanisms typically require a passenger to make contact with the seat back to initiate the breakover.